II-VI group compound semiconductor device and method for manufacturing the same

ABSTRACT

A II-VI group compound semiconductor device having a p-type Zn x  Mg 1-x  S y  Se 1-y  (0≦x≦1, 0≦y≦1) semiconductor layer, on which an electrode layer is formed with at least metallic nitride layer lying between the semiconductor layer and the electrode layer.

This application is a divisional of application Ser. No. 08/409,307filed Mar. 23, 1995, now U.S. Pat. No. 5,587,609.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a II-VI group compound semiconductordevice and a method for manufacturing the same. More particularly itrelates to a II-VI group compound semiconductor device having anelectrode structure with small contact resistance, especially anelectrode structure which enables an ohmic contact, and a method formanufacturing the same.

2. Description of the Prior Arts

So far various types of electrodes for a II-VI group compoundsemiconductor device have been studied. Haase et al., for example, haveexamined the applicability of Li, Na, Mg, Ti, Cr, Mn, Ni, Pd, Pt, Cu,Ag, Zn, Hg, Al, In, Sn, Pb, Sb or Bi and alloys thereof as electrodematerials ("Short wavelength II-VI laser diodes", Inst. Phys. Conf. Ser.No. 120 p.9). However electrode materials which provide ohmic contactsfor II-VI group compound semiconductors have not yet been found.

Thus, Au is extensively used as an electrode metal, but since Au forms aSchottky junction with approximately 1.2 eV of potential barrier top-type ZnSe, ohmic contacts have not yet been made.

In order to make the ohmic contact to, for example, p-type ZnSe,following methods are considered:

a low-energy-barrier intermediate layer of CdSe or HgSe is epitaxiallygrown between the electrode metal and p-type ZnSe, or

p-type ZnTe is used for the contact layer and a p-type ZnSeTe gradedcomposition layer or an intermediate layer of a p-type ZnSe/ZnTestrained-layer superlattice is used between the p-type ZnSe and p-typeZnTe.

Otsuka et al. have demonstrated an ohmic contact of Au/p-CdSe andreported the possibility of that of Au/pCdSe/p-ZnSe ("Growth andCharacterization of p-type CdSe", Otsuka et al., Extended Abstracts (the54th) p.255, The Japan Society of Applied Physics). Lansari et al. havemade a good ohmic contact by growing HgSe on p-type ZnSe as a low-energybarrier intermediate layer by MBE and using Au as an electrode metal(Improved ohmic contact for p-type ZnSe and related p-on-n diode), Y.Lansari et al., Appl. Phys. Lett. 61 p.2554). Fan et al. ("Gradedbandgap ohmic contact to p-ZnSe", Y. Fan et al., Appl. Phys. Lett. 61p.3160), and Hiei et al. ("Ohmic contact to p-type ZnSe using ZnTe/ZnSemultiquantum wells", F. Hiei et al., Electronics Lett. 29 P.878) havereported the fabrication of an ohmic contact by using p-type ZnTe forthe contact layer and using a p-type ZnSeTe graded composition layer orthe intermediate layer of a p-type ZnSe/ZnTe strained layer superlatticebetween the p-type ZnSe and p-type ZnTe.

However, none of the methods of making ohmic contacts to theconventional II-VI group compound semiconductors are satisfactory. Theyhave the problems below.

When CdSe is used, a low CdSe acceptor concentration of 1×10¹⁷ cm⁻³ inCdSe makes it difficult to lower contact resistance. When HgSe is used,the sharing of the MBE apparatus used for forming other layers in thedevice manufacturing process brings deteriorated properties of devicesbecause of the mixing of Hg atoms into other layers. Introducingexclusive MBE apparatus to avoid intermixing of atoms will conduct lowerproductivity. Furthermore, HgSe has poor chemical and physicalstability.

When ZnTe is used, the stress remaining in the film because of largelattice mismatch between ZnSe and ZnTe may deteriorate the properties ofdevices, and it is difficult to keep ZnTe carrier concentrationsuitable. A large lattice mismatch between ZnSe and any of the aboveintermediate layers also causes strain, and the epitaxial growth lowersthe productivity.

Furthermore, the Au electrodes used for the above methods are inferiorin mechanical strength such as adhesion.

Accordingly, research was continued to create an electrode structurewhich makes an ohmic contact to II-VI group compound semiconductors,especially to p-type Zn_(x) Mg_(1-x) S_(y) Se_(1-y) (0≦x≦1, 0≦y≦1)semiconductors.

FIG. 9 shows an ionized impurity concentration dependence of contactresistance of a metal/p-ZnSe Schottky junction as a parameter of thepotential barrier φ_(B) between the metal and p-type ZnSe. As shown inFIG. 10, the potential barrier φ_(B) is given by φ_(B) =x_(s) +E_(g)-φ_(M), in which x_(s) represents an electron affinity of semiconductor,E_(g) represents a bandgap of semiconductor and φ_(M) represents a workfunction of metal. FIG. 8 is a band diagram illustrating the Schottkybarrier at a contact interface when a p⁺ -ZnSe layer lies between themetal and p-type ZnSe. FIG. 9 shows what is obtained by a calculationusing the Yu model in which thermionic emission and tunneling currentsare considered ("Electron Tunneling and Contact Resistance of Metal-SiContact Barrier", A. Y. C. Yu, Solid State Electronics vol.13 p.239(1970)). As a result, the contact resistance decreases with the increaseof the ionized impurity concentration. This is due to the decrease ofSchottky barrier width (w), as shown in FIG. 8, with increasing ionizedimpurity concentration, which results in the rapid increase of tunnelingcurrent.

This is also the same between metal and p-type Zn_(x) Mg_(1-x) S_(y)Se_(1-y) (0≦x≦1, 0≦y≦1) semiconductors. For example, a figure showingthe dependence of contact resistance on impurity concentration (i.e.,corresponding to FIG. 9) shows a similar inclination in which thecontact resistance differs in one figure against the same potentialbarrier parameter.

In other words, an ohmic contact can be made by using a intermediatelayer having a high ionized impurity concentration on the p-type Zn_(x)Mg_(1-x) S_(y) Se_(1-y) (0≦x≦1, 0≦y≦1) semiconductor layer surface, onwhich metal electrodes are formed.

However, p-type Zn_(x) Mg_(1-x) S_(y) Se_(1-y) (0≦x≦1, 0≦y≦1)semiconductor film is formed only by MBE, and the ionized impurityconcentration is, at best in the order of 10¹⁷ cm⁻³. It is impossible toform a film with sufficiently high ionized impurity concentration tomake an ohmic contact.

SUMMARY OF THE INVENTION

The present invention provides a II-VI group compound semiconductordevice comprising a p-type Zn_(x) Mg_(1-x) S_(y) Se_(1-y) (0≦x≦1, 0≦y≦1)semiconductor layer, and an electrode layer formed on the semiconductorlayer through at least metallic nitride layer between the semiconductorlayer and electrode layer.

Further the present invention provides a method for manufacturing aII-VI group compound semiconductor device having a p-type Zn_(x)Mg_(1-x) S_(y) Se_(1-y) (0≦x≦1, 0≦y≦1) semiconductor layer whichcomprises forming the semiconductor layer on a substrate, dopingnitrogen during or after the growth of the semiconductor layer, formingan electrode on the resulting semiconductor layer by depositing a metalwith free energy change .increment.G of nitride formation lower than-100 KJ/mol or its intermetallic compound, optionally followed by anannealing.

An object of the present invention is to provide a II-VI group compoundsemiconductor device and a method for manufacturing the same whereinsmall contact resistance electrodes are available without directlyforming a p-type Zn_(x) Mg_(1-x) S_(y) Se_(1-y) (0≦x≦1, 0≦y≦1)semiconductor layer having a high ionized impurity concentration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view showing an embodiment of a II-VIgroup compound semiconductor device of the present invention.

FIG. 2 is an enlarged view of a p-type electrode in the semiconductordevice of FIG. 1.

FIG. 3 shows current-voltage characteristics of an Nb/p-ZnSe/p-GaAsstructure in an embodiment of a II-VI group compound semiconductordevice of the present invention.

FIG. 4 shows an annealing temperature dependence of differentialresistance value at 0 V of an Nb/p-ZnSe/p-GaAs structure of the presentinvention.

FIG. 5 shows an annealing time dependence of differential resistancevalue at 0 V of an Nb/p-ZnSe/p-GaAs structure of the present invention.

FIG. 6 shows current-optical output power characteristics andcurrent-voltage characteristics of a laser device as an embodiment ofthe present invention.

FIG. 7 is a schematic sectional view showing a II-VI group compoundsemiconductor device of the present invention.

FIG. 8 is a band diagram in which a high ionized impurity concentrationp-type Zn_(x) Mg_(1-x) S_(y) Se_(1-y) (0≦x≦1, 0≦y≦1) semiconductor layeris formed at the interface of metal/p-type Zn_(x) Mg_(1-x) S_(y)Se_(1-y).

FIG. 9 shows a graph illustrating ionized impurity concentrationdependence of contact resistance in a Schottky junction of a p-type ZnSewith a metal theoretically calculated with thermionic emission andtunneling current.

FIG. 10 is a band diagram showing the relationship: φ_(B) =x_(s) +E_(g)-φ_(M).

FIG. 11 is an AES in-depth profile taken from an undoped ZnSe epitaxiallayer cleaned by acetone solution.

FIG. 12 is an X-ray photoemission spectra of Se 3d electrons for ZnSeepitaxial layers cleaned by acetone and etched by SBW.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The semiconductor device of the present invention may include alight-emitting diode or a semiconductor laser as shown in FIG. 7.Basically, a p-type Zn_(x) Mg_(1-x) S_(y) Se_(1-y) (0≦x≦1, 0≦y≦1)semiconductor layer is formed on a substrate and an electrode through atleast a metallic nitride layer is formed on the semiconductor layer.

Example of the substrates are compound semiconductor substrates known inthe art, typically GaAs substrate.

Example of the p-type Zn_(x) Mg_(1-x) S_(y) Se_(1-y) (0≦x≦1, 0≦y≦1)semiconductor layers in the present invention includes ZnS (x=1, y=1),MgS (x=0, y=1), ZnSe (x=1, y=0), MgSe (x=0, y=0), ZnS_(y) Se_(1-y) (x=1,0<y<1), MgS_(y) Se_(1-y) (x=0, 0<y<1), Zn_(x) Mg_(1-x) S (0<x<1, y=1),Zn_(x) Mg_(1-x) Se (0<x<1, y=0), or Zn_(x) Mg_(1-x) S_(y) Se_(1-y)(0<x<1, 0<y<1). Preferably, the semiconductor layers are ZnSe (mostextensively used for contact layers), ZnS₀.07 Se₀.93 (latticed-matchedto GaAs) and ZnMgSSe (lattice-matched to GaAs and having not more than3.0 eV of bandgap energy and not less than 10¹⁷ cm⁻³ of effectiveacceptor concentration Na-Nd). The thickness of the semiconductor layeris e.g., in the range of 10-10,000 nm without limitation and can besuitably adjusted in accordance with use of the semiconductor device orthe like.

The metallic nitride layer intervened between the semiconductor layerand electrode layer is preferably a metallic nitride with more than 800°C. of melting point, such as NbN, VN, WN, TaN, MoN, HfN, ZrN, ScN, TiN,WTiN or WSiN, or a combination thereof such as NbVN, NbHfN, and ScVN.The metallic nitride layer can exert desired effects when it is amono-atomic layer, but is preferably those having not less than severalatomic layers in accordance with the surface roughness of thesemiconductor layer. This is because when the metallic nitride layer istoo thin it cannot compensate the surface roughness, which may leadundesirable direct contact of the semiconductor layer and the electrode.Thus it is preferable to form the metallic nitride layer so as tosufficiently cover all the surface of the semiconductor layer. Thethickness of the metallic nitride layer may be not more than 10 nmthick. When the metallic nitride layer is more than 10 nm thick, itcauses strain and crystal defect at the interface between the nitridelayer and the semiconductor layer or at the side of the semiconductorlayer, or separation of the interface of these two layers due to thedifference in lattice constant and thermal expansion coefficient ofthese two layers, thereby deteriorating the electrode property.Preferably, the metallic nitride layer is thin sufficient to allow freemovement of carriers between the semiconductor layer and the electrodeor to not substantially disturb the movement of carriers.

In order to form the metallic nitride layer, an advanced technique suchas MBE method is unnecessary. It is easily formed as a thin. layer bythe sputter method in which NbN, VN, WN, TaN, MoN, HfN, ZrN, ScN, TiN,CrN, WTiN or WSiN, or a combination thereof such as NbVN, NbHfN, ScVNand CrTaN is used as a target.

Materials for the electrode layer may be any materials used forelectrode in the art, such as Al, Pt, Mn, Cr, Nb, V, Ta, Zr, Mo, Hf, Zror W. The electrode can be formed by using conventional metal depositionmethods such as resistive heating evaporation, electron beam evaporationor sputter method. The thickness of the electrode layer is preferably inthe range of 10 to 10,000 nm.

The present invention provides a method for manufacturing a II-VI groupcompound semiconductor device having a p-type Zn_(x) Mg_(1-x) S_(y)Se_(1-y) (0≦x≦1, 0≦y≦1) semiconductor layer which comprises forming thesemiconductor layer on a substrate, doping nitrogen during or after thegrowth of the semiconductor layer, forming an electrode on the resultingsemiconductor layer by depositing a metal with free energy change.increment.G of nitride formation lower than -100 KJ/mol or itsintermetallic compound onto the semiconductor layer optionally followedby an annealing.

The semiconductor layer in the present invention can be formed by aknown method such as MBE, MOCVD or CVD method.

When the semiconductor layer is being formed e.g., by MBE method,nitrogen is preferably doped by nitrogen radical doping method to thesemiconductor layer. Further, nitrogen can be doped by sputter or ionplantation method to the semiconductor layer once formed. Theconcentration of nitrogen in the semiconductor layer may be not lessthan 1×10¹⁸ cm⁻³, preferably not less than 1×10¹⁹ cm⁻³.

Metals with free energy change .increment.G of nitride formation oflower than -100 kJ/mol and intermetallic compounds thereof can be usedfor the metal layer in the method for manufacturing a II-VI groupcompound semiconductor device of the present invention. Examples of themetals include Nb, V, Ta, Zr, Mo, Hf, Zr, W, or WTi, or an intermetalliccompound thereof.

The metal layer is formed by a conventional metal deposition method suchas resistive heating evaporation, electron beam evaporation or sputtermethod. It is preferable to use electron beam evaporation method,because the metal to be employed has a high melting point. In addition,the electron beam evaporation can increase the reactivity between themetal layer and the semiconductor layer because the metal has a highenergy and makes it easy to form the metallic nitride by the reaction ofthe semiconductor layer with the metal layer even at a relatively lowsubstrate heating temperature from room temperature to approximately300° C.

It is preferable to form the metal layer on the semiconductor layerafter removing native oxides or carbides formed on the surface of thesemiconductor layer. This is because the cleaning of the semiconductorlayer surface lowers contact resistance more efficiently, therebyproviding good ohmic characteristics with reproducibility. Native oxideand carbide can be removed, for example, by chemical etching solutioncontaining a saturated bromine water (SBW) before forming the metallayer. Thus the removal of the oxides and carbides from thesemiconductor surface makes it possible to form an electrode structurestably on clean semiconductor surface. When the metal layer is formedimmediately after the formation of the semiconductor layer (in situmethod), the cleaning step is omittable.

Furthermore, an annealing is preferably applied to the metal layer andsemiconductor layer after the metal layer is formed. When the metallayer is formed by electron beam evaporation method, it is possible todecrease the contact resistance and make ohmic contacts. However,annealing in respective of the kind of the metal layer formation methodcan increase nitride formation by the reaction of metal with nitrogen inthe semiconductor layer, decreases the contact resistance moreefficiently and makes better ohmic characteristics. Although the metallayer formed by resistive heating evaporation method usually does notshow sufficient ohmic characteristics, annealing can provides ohmiccharacteristics thereto.

The temperature for annealing should be in such that the metal and thedoped nitrogen can well react each to other and the property of thesemiconductor layer is not substantially deteriorated, typically in therange of 100° C.-300° C. This is because when MBE method is conductedbelow 300° C. for growing the semiconductor layer, annealing at atemperature above 300° C. tends to change the property of thesemiconductor device. The electric furnace annealing or RTA (RapidThermal Annealing) is available for the annealing.

In the semiconductor device of the present invention, since a metallicnitride layer is formed on the semiconductor layer, the nitrogen as aconstituent element of the metallic nitride layer and the nitrogen inthe semiconductor layer act as an acceptor in the semiconductor layer atthe interface between the metallic nitride layer and semiconductorlayer. As a result, the effective ionized impurity concentration on theinterface between the p-type Zn_(x) Mg_(1-x) S_(y) Se_(1-y) (0≦x≦1,0≦y≦1) semiconductor layer and metallic nitride layer increases, and thecontact resistance on this interface decreases.

The semiconductor device-of the present invention is based on the factthat when the semiconductor layer contains nitrogen, the metallicnitride layer formed on the p-type Zn_(x) Mg_(1-x) S_(y) Se_(1-y)(0≦x≦1, 0≦y≦1) semiconductor layer draws the nitrogen and activates itas an acceptor, and the fact that the nitrogen constituting the metallicnitride layer activates as an acceptor in the semiconductor layer.

Comparing to the band diagram in FIG. 8, the above metallic nitridelayer corresponds to a metal layer region 3, the part with high ionizedimpurity concentration in the above semiconductor layer corresponds to ap⁺ region 2, and the above semiconductor layer corresponds to a P region1.

The metallic nitride is chemically stable, makes bonding firmly with thep-type Zn_(x) Mg_(1-x) S_(y) Se_(1-y) (0≦x≦1, 0≦y≦1) semiconductorlayer, and makes it possible to obtain ohmic characteristics with goodmechanical strength. Because of its melting point higher than 800° C.,the metallic nitride is thermally stable and provides reliableelectrodes without deteriorating owing to the heat caused by currentinjection.

In accordance with the method for manufacturing the semiconductor deviceof the present invention, when a metal layer is formed without regard tothe forming method, the nitrogen in the p-type Zn_(x) Mg_(1-x) S_(y)Se_(1-y) (0≦x≦1, 0≦y≦1) semiconductor layer and the metal with small.increment.G in the metal layer or the intermetallic compound of themetals react on the interface, and form a nitride layer. At this time,the nitrogen in the semiconductor layer is drawn to the interface withthe metallic nitride layer, nitrogen concentration increases in thesemiconductor layer at the interface, and a p-type Zn_(x) Mg_(1-x) S_(y)Se_(1-y) (0≦x≦1, 0≦y≦1) semiconductor layer with higher ionized impurityconcentration is formed.

The power to draw nitrogen is determined by free energy change.increment.G of nitride formation. Accordingly, the more in minus numberthe free energy variation .increment.G is, the better it is. Since whenit is not less than -100 kJ/mol it cannot draw nitrogen atoms well, notmore than -100 kJ/mol is preferable.

The amount of nitrogen to be doped in the p-type Zn_(x) Mg_(1-x) S_(y)Se_(1-y) (0≦x≦1, 0≦y≦1) semiconductor layer may be not less than 1×10¹⁸cm⁻³, preferably not less than 1×10¹⁹ cm⁻³. As known by the result shownin FIG. 9, this is because contact resistance decreases steeply at notless than 1×10¹⁸ cm⁻³, more steeply at not less than 1×10¹⁹ cm⁻³, andnot less than this level of ionized impurity concentration ispreferable. In addition, this is because the doped nitrogen is onlyionized partially, the rate is tens of percentage order, and mainlynon-ionized nitrogen is drawn to the above interface, wh ere ionizationincreases as well as nitrogen concentration becomes higher than that ofthe originally doped nitrogen and the ionized impurity concentrationobtained at this part is the same as or more than that of the dopednitrogen. When a nitrogen-doped semiconduct or layer is used, includingthe above semiconductor device of the present invention, the amount tobe doped may be not less than 1×10¹⁸ cm⁻³, preferably not less than1×10¹⁹ cm⁻³ for the same reason.

Sinc e t he metal layer in the present invention contains a metal whichforms a compound with nitrogen or an intermetallic compound, the partbonded with the metallic nitride layer has a high adhesion, and enablesthe formation of stable electrodes. This material has a high meltingpoint of 600° C., and provides electrodes resistant to heat.

EXAMPLE

The semiconductor device and method for manufacturing the same isdescribed below.

Example 1

First, on a semi-insulated GaAs substrate was formed a nitrogen-dopedp-type ZnSe layer (Na-Nd=4×10¹⁷ cm⁻³ by MBE method with nitrogen radicaldoping. The surface of the p-type ZnSe layer was cleaned by ultrasonictreatment for 5 minutes in acetone and 2 minutes in ethanol, and wasetched for 3 minutes with saturated bromine water (SBW): hydrobromicacid (HBr): water (H₂)=1:10:90 at room temperature. By the etching, thep-type ZnSe layer surface was etched approximately 30 nm, and the oxidesand carbides on the surface of the p-type ZnSe layer were removed.

Next, an Nb layer was deposited on the p-type ZnSe layer by electronbeam evaporation maintaining a substrate temperature at roomtemperature. The electron beam evaporation was carried out at backgroundpressure in the range of 3×10⁻⁷ -5×10⁻⁷ Torr and at not more than 5×10⁻⁶Torr of vacuum during the deposition.

The Nb layer was 50 nm thick. Two electrodes with 1 mm diameter ofcircular planes were formed, and the distance between the centers of thetwo circles was 2 mm. An electric furnace annealing was carried out for7 minutes in the atmosphere of nitrogen: hydrogen=95:5.

Concerning the above-mentioned device having Nb circular electrodes witha distance of 2 mm between the electrode centers, current-voltagecharacteristics between the two electrodes were measured. FIG. 3 showsthe result. As seen in FIG. 3, the electrodes shows good ohmiccharacteristics.

The annealing temperature dependence of the differential resistancevalue at 0 V of the above sample was measured. FIG. 4 shows the result.As seen in FIG. 4, the resistance value decreased with increasingannealing temperature, reached a minimum at 260° C., and increasedgradually at the temperatures higher than 260° C.

The annealing time dependence of the differential resistance value at 0V of a sample with the same structure was measured. The result is shownin FIG. 5. Annealing temperature was 260° C. The differential resistancevalue decreased rapidly for 10 minutes after beginning, and decreasedslowly after that. Not less than 10 minutes is preferable to make asufficiently low resistance in a short while.

Table 1 shows the free energy change .increment.G of nitride formationand melting points of several metals.

                  TABLE 1                                                         ______________________________________                                        METALS     ΔG (KJ/mol)                                                                       MELTING POINTS (°C.)                              ______________________________________                                        Mn          -24      1260                                                     Cr          -28      1800                                                     V          -103      1735                                                     Ta         -148      3000                                                     Nb         -207      2500                                                     Zr         -250      1750                                                     ______________________________________                                    

In the metals shown above, as comparative examples, Mn and Cr, which arefree energy change .increment.G of nitride formation lower than -100kJ/mol were used for the metal layer to make the same electrodes as theabove in the same way and to measure the current-voltage characteristicsbetween the two electrodes. The Mn and Cr did not provide good ohmiccontacts.

Example 2

A II-VI group compound semiconductor device (laser) in accordance withthe present invention is shown below. The laser device structurecomprises, on an n-type GaAs substrate 1, an n-type ZnS₀.07 Se₀.93buffer layer 2 (0.1 μm of layer thickness, Nd-Na=1×10¹⁸ cm⁻³), an n-typeZn₀.91 Mg₀.09 S₀.12 Se₀.88 cladding layer 3, (1.0 μm of layer thickness,Nd-Na=5×10¹⁷ cm⁻³), an n-type ZnS₀.07 Se₀.93 optical waveguide layer 4(0.1 μm of layer thickness, Nd-Na=5×10¹⁷ cm⁻³), a Zn₀.8 Cd₀.2 Se activelayer 5 (7.5 nm of layer thickness), a p-type ZnS₀.07 Se₀.93 opticalwaveguide layer 6 (0.1 μm of layer thickness, Na-Nd=5×10¹⁷ cm⁻³), ap-type Zn₀.91 Mg₀.09 S₀.12 Se₀.88 cladding layer 7 (1.5 μm of layerthickness, Na-Nd=5×10¹⁷ cm⁻³), a p-type ZnSe contact layer 8 (0.1 μm oflayer thickness, Na-Nd=2×10¹⁸ cm⁻³), a p-type electrode 9, an n-typeelectrode 11 and a polyimide buried layer 10. MBE method was used toform the above semiconductor layers, namely the buffer layer 2, claddinglayer 3, optical waveguide layer 4, active layer 5, optical waveguidelayer 6, cladding layer 7 and contact layer 8.

The electrode part on the p-type side comprises an Nb layer 13 depositedon the p-type ZnSe contact layer 8 by electron beam evaporation at roomtemperature, and an NbN layer 12 formed by the reaction of the Nb layer13 during the deposition and by annealing after the deposition (FIG. 2).The electron beam evaporation was carried out maintaining the substratetemperature at room temperature and at background pressure in the rangeof 3×10⁻⁷ -5×10⁻⁷ Torr and at not more than 5×10⁻⁶ Torr of vacuum duringthe deposition. The layer thickness of the Nb layer 13 was 50 nm. Beforeforming the Nb layer 13, the surface of the p-type ZnSe contact layer 8was cleaned by ultrasonic treatment for 5 minutes in acetone and 2minutes in ethanol, and etched for 3 minutes with saturated brominewater (SBW): hydrobromic acid (HBr): water (H₂ O)=1:10:90 as an etchantat room temperature. By the etching, the surface of the p-type ZnSecontact layer was etched at approximately 30 nm, and the oxides andcarbides on the surface were removed. After forming the Nb layer 13, thedevice was annealed by electric furnace at 260° C. for 7 minutes in theatmosphere of nitrogen: hydrogen=95:5. In order to prevent thedeterioration of device properties, annealing at not more than 300° C.is preferable. Then the structure in FIG. 1 was completed by forming then-type side electrode 11 and polyimide buried layer 10. The Nb electrodeobtained in this way was more excellent in adhesion than an electrodeformed by Au instead of Nb in the same structure.

Example 3

A laser device with 1 mm cavity length was made of the laser structurein FIG. 1 (stripe width: 5 μm) by cleavage. The laser device was set ona.copper heat sink with a junction-up configuration, and thecurrent-optical output characteristics and current-voltagecharacteristics of the device by CW operation were measured at roomtemperature. The end of the laser device cavity had no coating and keptcleaved.

FIG. 6 shows the cuurent-optical output characteristics andcurrent-voltage characteristics of the laser device. As shown in FIG. 6,20 mA of threshold current and 3.4 V of threshold level voltage wereobtained.

On the other hand, when the p-type electrode 9 was formed of an Auelectrode, the voltage was not less than 10 V, and when the p-type sideelectrode 9 was formed of a Au/ZnTe/ZnSe-ZnTe-electrode structure by Fanet al. ("Continuous-wave, room temperature, ridge waveguide green-bluediode laser", A. Salokatve et al., Electronics Lett. Vol. 29 p.2192), itwas 4.4 V.

Example 4

A nitrogen-doped p-type ZnSe, ZnS₀.2 Se₀.8 (Na-Nd=2×10¹⁷ cm⁻³), Zn₀.91Mg₀.09 S₀.12 Se₀.78 (Na-Nd=5×10¹⁷ cm⁻³), Zn₀.91 Mg₀.09 Se (Na-Nd=5×10¹⁷cm⁻³) which were formed on a semi-insulated GaAs substrate by MBE methodwith nitrogen radical doping and the surface of the above four p-typelayers were cleaned in the same way as in Example 1.

Next, the semi-insulated GaAs substrate on which the above four layerswere formed respectively by resistive heat evaporation, were kept atroom temperature, 50 nm of Zr layer was deposited by electron beamevaporation on the above four layers to form an electrode, respectively.

Example 5

AES characterization of ZnSe surfaces

In order to understand the effect of SBW etching, ZnSe surfaces of apolycrystalline substrate and an epitaxial layer grown by MBE methodwere analyzed by Auger electron spectroscopy (AES).

FIG. 11 represents AES in-depth profiles taken from an undoped ZnSeepitaxial layer cleaned by acetone solution. Carbon and oxygen areclearly observed within about 2 nm thickness from the surface of thelayer. The AES analysis reveals that there exists a thin dielectriclayer composed of oxygen and carbon on the ZnSe surface.

FIG. 12 is X-ray photoemission spectra of Se 3d electrons for ZnSeepitaxial layers cleaned by acetone solution (described simply asacetone surface) and SBW etching for 3 minutes (described as SBWsurface). A weak Se 3d peak corresponding to the Se--O bond with abinding energy of 62 eV is observed on the acetone surface in FIG. 12,which gives the evidence of the existence of selenium oxide (which maybe presumably SeO₂). A strong Se 3d peak corresponding to the ZnSe bondin FIG. 12 is constructed form multiple peaks of Se 3d_(3/2) with abinding energy of 56.9 eV and Se 3d_(5/2) with 56.2 eV. A broad peak inthe lower energy side at 48 eV is due to the spin-orbit interactionbetween 3d electrons. It should be noted that the Se 3d peak relatedwith the selenium oxide disappears on the SBW surface, indicating theremoval of selenium oxide.

The present invention provides a blue light-emitting device with loweroperating voltage than the devices using conventional electrodestructures.

What we claim is:
 1. A method for manufacturing a II-VI group compoundsemiconductor device having a p-type Zn_(x) Mg_(1-x) S_(y) Se_(1-y)(0≦x≦1, 0≦y≦1) semiconductor layer which comprises forming thesemiconductor layer on a substrate, doping nitrogen during or after thegrowth of the semiconductor layer, forming an electrode on the resultingsemiconductor layer by depositing a metal, or an intermetallic compoundof said metal, with the free energy change .increment.G of nitrideformation lower than -100 kJ/mol.
 2. A method for manufacturing a II-VIgroup compound semiconductor device as set forth in claim 1, whereinnative oxide or carbide on the surface of the semiconductor layer isremoved before the deposition of the metal or intermetallic compound. 3.A method for manufacturing a II-VI group compound semiconductor deviceas set forth in claim 1, further comprising an annealing.
 4. A methodfor manufacturing a II-VI group compound semiconductor device as setforth in claim 3 wherein the annealing is conducted at a temperaturebelow 300° C.